Developing a Summer Stress Fungicide Program for Coachella Bentgrass (and the Case of the Mysterious #13)

This is a follow up on something I been meaning to address but spurred on by an email I received this week:

Dr. Wong,

I am a Golf Course Superintendent in the Palm Springs area and manage Penncross putting greens. As we both know, heat and cool-season grasses don’t work well together.

Currently we are experiencing exceptional summer bentgrass decline due to high heat and humidity. Are there any fungicide trials or protocols that other Superintendents may be using to minimize effects of SBD? We have fans on each greens, and water as needed with syringing during the day. Our heights are .150 and mowed every other day. Other than that we try to keep them alive.

Hot in Coachella

Yes, bentgrass and triple digit temperatures through the summer get along as well as Meg Whitman and Jerry Brown in California. Based on work done at NC State by Turfgrass Specialist Art Bruneau, cool season turfgrass growth pretty much declines rapidly when 4-inch deep soil temperatures reach 70°F with root and shoot growth completely shutting down at 77ºF and 90ºF, respectively.

With soil temps in the California desert hitting 70 to 90ºF from April to September, it means a long late spring through the fall of tough conditions for superintendents in the desert (including other areas in the SW like Arizona, New Mexico and Nevada) who have to hold onto their bentgrass year round.

Although fighting Mother Nature through this period can be partially successful using fans and syringing; in any case, simply put the high temperatures will result in poor growth and recovery from the bentgrass magnifying any damage caused to the turf by mechanical, environmental or pest stress.

From a pathologist’s point of view, the diseases that would likely cause the most damage to bentgrass in this climate would be takeall patch, Pythium blight , Curvularia blight and algae.

Month

Avg. Hi

Avg. Low

Avg. Prec.

Jan

70°F

44°F

1.27 in.

Feb

75°F

47°F

1.15 in.

Mar

80°F

51°F

0.63 in.

Apr

88°F

56°F

0.08 in.

May

95°F

63°F

0.06 in.

Jun

104°F

70°F

0.05 in.

Jul

108°F

76°F

0.19 in.

Aug

107°F

76°F

0.40 in.

Sep

101°F

71°F

0.39 in.

Oct

91°F

61°F

0.11 in.

Nov

78°F

50°F

0.29 in.

Dec

70°F

43°F

0.61 in.

Take all typically infects and damages plants in cool wet weather through the fall and winter. Symptoms can often show up under periods of heat stress because plants with damaged roots simply can’t efficiently use water to keep themselves alive. In the desert, the high temps really hamper the ability of the turfgrass to recover and regrow, magnifying take all damage on bentgrass greens. I won’t cover it much here, but soil pH and manganese management coupled with preventive fall fungicide applications work best for preventing problems with take all.

Pythium blight is a real threat to cool season turfgrass when night time temperatures stay above 68ºF and there’s adequate moisture to trigger fungal growth and spread. There’s an excellent review of Pythium here at the Rutgers website:

Believe it or not, but Curvularia blight is pretty common to find on bentgrass coming from the desert. Curvularia can often be considered a wimpy disease that only attacks weakened or nearly dead bentgrass, but like anthracnoseon Poa, it can be the nail that closes the coffin on your summer stressed bentgrass if not controlled.

Alage can also turn up commonly as it’s quick to colonize wet surfaces and thinned out bentgrass in the summer.

The question posed by several Coachella Valley superintendents has been “how well does #13 work in California?”

Well, Bruce’s #13 provides broad spectrum protection vs. a number of summer diseases while using some of Bayer’s “Stress Gard” pigmented materials, and Insignia which BASF is reporting to promote plant health. But….the southeast gets a lot more humidity and #13 is also designed to pick up brown patch and dollar spot; it’s just too dry in Coachella to have these figure as major players in a summer disease profile.

Looking at #13, applications start in late May in the southeast and go at 14-day intervals; here’s the break down with likely targets of activity.

OK – if you discount the presence of dollar spot and brown patch in Coachella, you can see some of these applications would not be necessarily applicable. Also with regard to Tartan which is a mix of Compass and Bayleton, applying a DMI (Bayleton) isn’t necessary, especially if dollar spot pressure is absent. Spectro probably isn’t needed as much, again due to the lack of dollar spot and brown patch pressure.

Pythium pressure is likely to come from June through September with high night time temperatures. Insignia and Signature + Daconil applications would probably give some significant benefits during this time for both Pythium and “plant health benefits”. Although other Pythium-specific fungicides like Subdue, Banol and Stellar could be used, I would save these for overseeding type situations or when you know that hot wet weather is coming. Otherwise, it may be fine to rely on preventive applications of Signature or other phosphonate/phosphite type products during the summer. Although many of the phosphonate or phosphite type products do a very good job of controlling pythium and improving plant health, the “Stress Gard” pigment in Signature is something I think works pretty well as an added layer of stress relief for your turf.

I’d see Curvularia as a constant threat through the season, but it may not be worth using a 26GT application specifically for this disease, when you can get control with other materials.

A contact fungicide like mancozeb (Fore) may work just fine in Coachella for keeping pathogens like Curvularia at bay, plus beating back algae.

So…in putting all of this together, I’d say that #13 is a great program, but not necessarily well fit for southwestern desert bentgrass greens.

Looking at the situation, maybe something like this would work:

May 15: Fore 8 oz

Jun 1: Insignia 0.9 oz

Jun 15: Fore 8 oz

Jul 1: Signature 4.0 oz + Daconil Ultrex 3.2 oz

Jul 15: Insignia 0.9 oz

Aug 1: Signature 4.0 oz + Daconil Ultrex 3.2 oz

Aug 15: Fore 8 oz

Sep 1: Signature 4.0 oz + Daconil Ultrex 3.2 oz

Sep 15: Fore 8 oz

Keeping the Signature and Daconil in the mix as a stress & algae application; Insignia as a 28-day preventive early in the summer and regular applications of Fore to clean up algae and clean up “junk” diseases like Curvularia may work just fine.

I’d like to see some research in Coachella to support the suggestions, but this type of program may be a good starting point. If you think "there goes Dr. Wong, smoking the crack again." - that's fine too; I think it's good to have some discussion about what is working for guys in the desert who are growing bentgrass.

Bottom line: programs like #13, are very good, but may not cover the diseases & stresses unique to the southwest – think about what you’re trying to fight and design a program around that.

A Few Thoughts about Nematodes

One thing that needs some attention as far as bentgrass greens in Coachella is the presence of some new root knot nemtaodes found affecting cool season turf. Very high populations were associated with severe damage at a few locations in Coachella in 2009. As discussed above, the summer stress for growing creeping bentgrass in Coachella is already pretty high – nematode populations really need to be considered in this equation.

This is a green from 2009 in Coachella that took some severe nematode damage; don't let this be you!

If you’re growing bentgrass in the Valley; it’d be worth having a test done to see if you need to worry abouyt these critters as well.

Unfortunately, I don't think you can post pictures in comments, but if you email them to me at my regular UCR address (see www.turfpathology.ucr.edu) , I can post them for you on blogspot.

OK - as far as nematodes, root knot and other soil inhabiting nematodes can be all over the place and the "new" one in Coachella was only found because someone started looking. Best bet - get a nematode test done to see if you have them or what you have.